Method and apparatus for production of structures



Aug. 9, 1941. G. DE w. GRAVES 2,253,176

una'rnon AND APPARATUS FOR PRODUCTION OF STRUCTURES Filed Aug. 9, 193a George D6 Wz'z'ffiraves INVENTOR BY W ATTORNEY these dimculties result Patented Aug. 19, 1941 DIETHOD AND APPARATUS FOR PRODUC- IION OF STRUCTURES George De Witt Graves, Wilmington, DeL, as-

signor to E. Wilmington,

I. du Pont de Nemours & Company,

DcL, a corporation of Delaware Application August 9, 1938, Serial No. 223,937

15. Claims.

This invention relates to the production of yarns, filaments, ribbons and the like. More particularly, it relatesto' the melt spinning of yarns, filaments, ribbons, and the like from organic filament-forming compositions which have a tendency to change theirchemical composition while in the molten state. i

The spinning of filaments from molten filament-forming com sitions is a relativelynew art and presents numerous difficulties. Some of from the decomposition of the filament-forming compositions contemplated. This decomposition is objectionable not only because of thedegradation of the filamentforming compositionwith its accompanying effect upon the propertiesof the filaments produced but also because it often results inthe formation of gaseous products which form bubbles in the molten filament-forming composition. The pres.- ence of these bubbles results in filaments of nonuniform denier since the gaseous component is metered along with the molten filament-forming composition prior to extrusion. Likewise this cosity of the filament-forming composition which may also result in a change in denier. Similarly, in the melt spinning of certain organic filamentforming compositions of a polymeric nature, further polymerization may occur at the temperature of melt spinning so that the viscosity is raised and other properties affected. Likewise, slight differences in the extruded filaments are likely to produce large dyeing-differences in the finished product. Frequently, two or more of ,these effects may occur simultaneously. It is,

therefore, impossible to compensate for these changes by careful control of temperature, rate of metering, pressure, rate of draw-off of the extruded filaments, etc. and obtain filaments of very uniform quality and denier.

It is, therefore, an object of this invention to provide an improved method and apparatus for the melt spinning of filaments from organic filasition is melted at a rapid rate.

. decomposition often results in a change of vis- Other objects of the invention will appear hereinafter.

The objects of this invention are accomplished, in general, by feeding the solid organic filamentforming composition on to a heated surface upon which melting occurs at a rate substantially equal to the rate of withdrawal of the molten composition, and allowing the molten filamentforming composition to flow to a pool of restricted volume from which the molten filament-forming composition may be withdrawn, for example, by forcing the same through an opening of a desired size and shape, solidifying the formed composition, and collecting the solidifiedarticles in any desired manner.

In order to more clearly define the present invention, reference is made to the following detailed description taken in connection with the accompanying illustration, in which:

Figure 1 is a diagrammatic, side elevational view of an apparatus for melt spinning according to the invention.

Figure 2 is a similar view of another modification of the invention.

Figure 3 and Figure 4 are diagrammatic, side elevational views showing modified forms of the grid melting unit used in the present invention. In Figure 1, reference numeral H represents a cylindrical chamber which may be insulated or which maybe provided with means for heating the same. fiat spiral metal coil or grid l2. The grid l2 is constructed of tubing and is preferably constructed from a non-corrosive metal such as stainless steel, Monel, illium or similar metal H alloy. The spiral coil grid l2 may be heated by means of electrical resistance units positioned at the interior thereof or by means of a heating medium circulated therethrough, Solid pieces, e. g., flakes l5 of the organic filament-forming composition shown at iii are allowed to fall, preferably at a uniform rate, from the fiake hopper I! located above the chamber. If desired, an atmosphere of an inert gas may be main- The chamber II is provided with a substantially the same rate;

tained in the chamber ll. These flakes come to rest on the surface of the grid II, which is heated to a temperature above the melting point of the organic filament-forming composition. The flakes melt on the surface of the grid l2 and the molten filament-forming composition drains between the turns of the grid and is shown dropping at Hi to the pool II from whence it may be withdrawn in any desired manner such as by means of a pumping element, e. g., a gear metering pump, for example, a pump similar to the type commonly used in the spinning of filaments from viscose, which meters it to the spinneret from which it is forced in the form of filaments, ribbons or the like.

For the most satisfactory operation of the invention, these flakes shown at l5 should be of essentially uniform size andof somewhatlarger size than the spaces between turns of the melting grid l2. unmelted material falling throughv the grid. It is to be noted, however, that once melting has begun and the viscous, molten filament-forming composition is draining through the grid, flakes do not tend to fall through unmelted even though they be somewhat smaller than the grid separation since they are caught in the viscous mass. While the separation of the turns of the grid can be varied over considerable limits depending on the size of the flakes or chips of the filamentforming composition, the minimum separation of the turns of the grid is critical and is dependent on the viscosity of the molten filament-forming composition. If the turns of the grid are too closely spaced the molten material does not drain properly. It is, therefore, necessary to provide grid turns with sufficient separations to permit proper draining of the molten filament-forming composition and to provide flakes of the solid filament-forming composition of proper size relative to the grid separation.

Not only is it important that the flakes of filament-forming composition have a certain minimum size but it is also important that they be of a uniform size and only slightly larger than the spaces between the turns of the grid. There are several reasons for this: To achieve uniform melting and minimum exposure to the elevated temperature it is desired that a maximum surface area of the flake be in contact with the melting grid, which is attained by minimum flake size; to obtain melting at a uniform rate, which is vital to the invention, the particles should be of uniform size in order that they will melt at and likewise the feeding of the flakes to the melting grid is facilitated by the use of small uniformly sized flakes. Flakes suitable for use in this invention can be conveniently prepared by a process disclosed in the applicants copending application Serial No. 223,998 filed of even date herewith.

It is usually preferable to provide a melting unit for each spinneret since it is desired to maintain a minimum quantity of the filamentforming composition in the molten condition. It is to be understood, however, that the invention is not so limited, for by placing a plurality of spinnerets in close proximity to the melting grid, supplied by a rapid parallel or a circulating series flow through restricted passages or by other special means, one melting unit could supply a plurality of spinnerets.

While it might be expected that as each individual flake melts, and its size decreases, a solid residue would drop into the pool below unmelt- This eliminates any possibility of ed, this is not the case. The viscosity and other physical properties of molten organic filamentforming compositions are such that the solid particle adheres to the grid surface until it is completely melted.

Although the rate at which the flakes are fed to the grid may be accurately adjusted to the rate of extrusion of the molten filament-forming composition, it is desirable to know the quantity of liquid material present in the pool at all times, since an object of the invention is to obtain minimum exposure of the molten material to elevated temperatures. This may be done in a number of ways as by the use of gauges, windows, and the like. A particularly convenient method of determining the quantity of liquid in the molten pool is by means of a conductivity measurement, since organic filament-forming compositions exhibit sufilclent electrical conductivity for such a measurement. This may be done by inserting a vertical electrode l8 through the bottom of the melt chamber H by means of suitable insulation 20. This electrode is connected through a suitably calibrated milliammeter 22 to a battery 24 or other power source and thence connected to the walls of the melt chamber which comprise the other electrode. The circuit is completed through the molten filament-forming composition. A rise in level is ac companied by an accompanying increase in the flow of current.

In accordance with the present invention, it is preferred to restrict the amount of molten fllament-forming composition in the pool to the minimum quantity required to continuously supply the spinneret or other extruding means. The maximum volume permissible depends to a large extent on the nature of the filament-forming composition and the rate of extrusion. In general, it is preferred that the volume does not exceed that which will be withdrawn from the pool in one hour, and more preferably in 15 minutes.

Another modification of the invention is shown in Figure 2. In this figure, reference numeral 26 represents a cylindrical chamber preferably heated internally by passing a hot vapor, e. g., steam at high pressures, or Dowtherm, through the passages represented at 28. A melting grid 30, preferably composed of metal, is heated internally, for example, by the passage therethrough of a hot vapor. The melting grid 30 is provided with a metal plate 32 covering the open space left by the last turn of the coil. The unheated cylindrical chamber 34 is filled with the flakes of filament-forming composition. The chamber 3| is preferably provided with a closure 36. In many instances, it is desired to preheat the flakes of filament-forming composition in this chamber. This increases the rate of melting when the flakes reach the grid and removes any excess moisture which may have condensed on the flake.

, forming composition. A hopper 38 is positioned below the grid 30. The molten filament-forming into the hopper 38 after melting on and draining through the grid 30. This molten filament-forming composition then flows from the hopper 38 through the passage 40 to the gear metering pump 42 from which it is forced to the spinneret pack 44 and spinneret 46 through conduit 48. The molten material is ex- This modification of hopper '38, through arcane in the form of If it'is desired truded through the spinneret 4U filaments, ribbons, and the like.

to maintain an atmosphere of an inert gasin gas at 50 and removing it by Hand. a

the invention differs from that described in Figure 1 since the melt level is automatically maintained. As a solid body of the flakes is fed to the melting grid, melting ocours and the hopper 38 becomes completely filled. Further melting results in the formation of a thin layer of the molten filament-forming composition above heat conductivity of the molten materialis very low, insumcient heat is transferred through this thinlayer of molten material to melt the solid above. Consequently, no further melting occurs until sufiicient molten material has been displaced by spinning to permit the level to fall below the level of the grid and to permit the solid filament-forming material to come; into" contact with the grid. This construction of the maintenance of a constant apparatus allows the minimum quantity of the molten material;

When spinning at a constant rate, the molten material is discharged at a constant rate so that it is exposed toan elevated temperature for a constant minimum length of time. In this modification the minimum size of the flakes is not so critical since the solid pieces tend to float and so do not get into the pool below the melting grid. i V V The process, with particular reference to the apparatus shown in Figure 2, will now be described more specifically with reference to the melt spinning of polyhexamethylene adipamide,-

a fiber-forming linear polyamideobtainable by the condensation polymerization of hexamethylene diamine and adipic acid and which has. a melting point of about 265. C. l

Flakes of polyhexamethylene adipamide approximately x /4" x were placed in the chamber 34 completely filling it and the space in the chamber 28 above the melting the inert gas permitted the maintenance of an.

inert atmosphere throughout the chamber and its passage in the proximity of the grid sweeps.

out any gases liberated upon melting. A presthe melting grid. Since the.

rid 30. The flakes rested on the melting grid, which was constructed from y," stainless steel tubing, the

.as rapidly as the spinning was continuously maintained.

As soon as the melt pool in hopper a was filled, a thin layer of molten material formed on the surface of thegrid lb and due to the low heat conductivity of the molten material no further melting occurred until the level dropped to that of the grid. As a result, the flakes-melted only position wasspun and a constant quantity of melt was automatically maintained.

In all of the modifications of the present invention, the molten filament-forming composition continuously drains from the melting surface. This downwardfiow of melt washes from i the melting surface any stagnant film. which sure of 10 lbs. of N: per square inch was maintained inside the chamber to prevent any diffusion of air into the apparatus. The flow of gas thus permitted replenishing the supply of the flakes without interrupting spinning.

The passages ing grid 30 were maintained at 285C. The flakes in contact with the grid melted and the filament-l-forming composition drained into the 4 the passage 40. to the gear pum 42 V 44 and spinneret 46' of filaments. The total volume of the pool in and 'spinneret pack.

c. c. so that sufllclent molten filament-formin 2s in chamber as andthe meltwhich forced it to the spinneretpack r from which it was spun at a rate of about 15 grams per minute inthe form tends to collect, thereby contributing to the uniformity of the melt and decreasing the possibility of decomposition.

While grid melting units spirally shaped and heated by electrical resistance or heated internally by circulation of a hot fiuid have been described, the invention is not so limited. The grid melting unit may take the form of a hollow cone 60 formed from rods or tubing as shown in Figure 3. In this modification, it may be desirable to provide the top of they cone with a cap 62. Similarly, the grid melting unit may comprise a pair of perforated metal discs 64 wedged against the side walls of the melt chamber 65, as shown in Figure 4. A plurality of tubes 58 may be arranged between the discs 64. Such discs 64 and tubes 68 can be heated by conduction of heat from the outside of the melting particles. Where spiral grids are used they may be formedfrom more than one circuit of pipe. Likewise, in some instances, it may be desirable to use more than one grid, or a second heating element may be immersed in the liquid pool to maintain it at any desired temperature.

The melting grids, in accordance with the present invention, may be maintained at any suitable temperature; preferably however, the melting grids are maintained at a temperature not to exceed 40 C.above the melting point of the filament-forming composition being spun.

While specific reference has been made to the use of a gear pump for forcing the molten fila- -ment-forrning composition to the spinneret, the

invention is not so limited. Use may be made of screw pumps, piston pumps, or pumps of any other type or gas pressure may be used for this purpose. If desired, use may be made of a combination of two pumps of the same or different types in series or combinations of gas pressure and pumps. I

As indicatedabove, in many cases, it may be preferable to maintain an inert atmosphere in the melt chamber, to prevent or reduce oxidation of the molten filament-forming composition. Nitrogen, carbon dioxide, hydrogen or any other oxygen-free gas which is inert to thefilamentforming composition, may be used for this purpose. The gas may be introduced at any convenient point in the melt chamber to maintain molten filament-forming comsuch an atmosphere. If desired, the face of the spinneret may be similarly blanketed to prevent oxidation of the freshly extruded filaments with accompanying interruption of the spinning.

Many other variations can be made in the specific details above set forth, for example, it may be desirable under certain circumstances to melt the filament-forming material at a temperature' well above the melting point and cool the molten compositionbefore it is extruded, thus increasing the speed of'melting with a minimum of decomposition.

In the foregoing description this invention has been illustrated with special reference to the spinning of polyhexamethylene adipamide but it is not so limited.

This invention is peculiarly adaptable to the spinning from melt of filaments and the like from these fiber forming synthetic linear polymers and particularly to the synthetic linear polyamides which belong to this class since these synthetic linear polymers are crystalline in the solid state as evidenced by X-ray investigation and they have a definite melting point. These synthetic linear polymers melt sharply, forming liquids which drain readily from the melting grid thus facilitating control of the melting and reducing any tendency to decompose at elevated temperatures. Other synthetic linear polymers include the polyesters, polyethers, polyacetals, mixed polyester-polyamides, etc. which, for example, may be prepared by a process of condensation polymerization as described in U. S. Patent No. 2,071,250.

My invention is also applicable to advantage in the spinning from melt of filament and .the like, of the polymers prepared by the high pressure polymerization of ethylene which are more fully described in the copending application of Fawcett, Gibson and Perrin, Serial Number 123,722 filed February 2, 1937 since they are also crystalline in the solid state. I

This invention is also applicable to the spinning of other organic filament forming compositions which are capable of being spun from melt particularly to the extruding of such materials which have a tendency to change their chemical composition while in their molten state. As examples of such filament forming compositions may be mentioned vinyl polymers, polystyrene and polyacrylic acid derivatives. Cellulose derivatives, e. g., cellulose acetate suitably plasticized can also be spun according to the invention.

- The present invention, furthermore, is not to be limited to the spinning of ribbons and filaments; the molten material may, for example, be withdrawn for the continuous coating of articles such as wire with synthetic linear polymers whereby to electrically insulate the same. The filament-forming material used in the process of this invention may contain modifying agents, e. g., luster modifying agents, plasticizers, pigments, dyes, antioxidants, resins, etc.

By practice of this invention, the solid filament-forming composition is melted rapidly and continuously whereupon the molten filamentforming composition drains directly to a pool of restricted volume from which it is extruded in the form of filaments, ribbons, and the like. Since the filament-forming composition is exposed to an elevated temperature for a minimum, constant period. any tendency toward decomposition, the formation of gaseous products and any tendency to polymerize further is reduced uniform physical to a minimum or is maintained at a constant rate. It is possible, therefore, to obtain in a continuous manner molten organic filamentforming compositions having uniform properties and to extrude these molten filament-forming compositions in a uniform and continuous manner in the form 01' yarns, filaments, ribbons, and

the like. By collecting the freshly spun flla-' ments in an orderly manner, filaments will be obtained of extremely uniform denier and of and chemical characteristics.

Since it is obvious that many changes and modifications can be made in the above detailed description without departing from the nature and spirit of the invention, it is to be understood that the invention is not to be limited except as set forth in the appended claims.

I claim:

1. In an apparatus for the melt spinning of structures from an organic filament-forming composition, a grid having a plurality of openings therein, means for heating said grid to a temperature above the melting point of said composition, means for feeding solid particles of composition on to said grid, means for collecting the liquid molten composition in the form of a pool, and pumping means for forcing said composition to a spinning unit.

2. In an apparatus for the melt spinning of structures from an organic filament-forming composition, a grid having a plurality of openings therein, means for heating said grid to a temperature above the melting point of said composition, means for feeding solid particles of said composition on to said grid, a spinneret, and pumping means for extruding said molten composition through said spinneret.

3. In an apparatus structures from an 4. In an apparatus for the melt spinning of structures from an organic filament-forming composition, an enclosure, a grid melting unit in said enclosure, means for conducting solid organic filament-forming composition onto said said extrusion means.

5. In an apparatus for the melt spinning of structures from an organic filament-forming composition, an enclosure, a grid melting unit in said enclosure, means for conducting solid organic filament-forming composition onto said which the grid is a spiral structure, the elements forming the spiral structure being spaced from each other to provide openings therebetween.

7. In an apparatus as set forth in claim 4 in composition to provide a substantially constant volume oiflow of said liquid composition through said extrusion means, conduit means connected to said solid conducting means, additional conduit means connected to said enclosure, said several conduit means adapted to pass an inert gas about said solid as the latter is conducted to the said unit. a

9. In an apparatus for the melt spinning oi structures ,from an organic filament-forming composition, an enclosure, a grid melting unit in said enclosure, means for conducting solid organic fllamentiorming composition onto said unit, means through which the liquid molten composition is extruded, collecting means, intermediate saidunit and extrusion means, for collecting a suilicient quantity of liquid molten composition to provide a substantially constant volume of ilow of said liquid composition through said extrusion means, and inert gas conveying means connected to said solid conducting means and said enclosure tor sweeping objectionable gaseous elements from said enclosure.

10. In an apparatus as defined in claim 1, means for maintaining an inert gas in contact with the melting and melted composition.

11. In a process for the melt spinning of a yarn from a molten synthetic linear polyamide spinning composition, the steps comprising continuously melting small solid particles of said composition in at atmosphere consisting of a gas inert to said composition, and continuously extruding the molten composition, the melting and extruding oi the composition being carried out at a temperature not to exceed 40 C. above the melting point of the composition, and the melting of said composition being carried out at a rate substantially equal to the rate of extrusion of said composition.

12., In a process for the melt spinning of structures from a molten organic filament-forming composition, the steps comprising passing small,

solid particles of said composition on to a heated surface to melt the same, passing an oxygeniree gas through said particles, extruding theresuiting molten composition, the melting of said composition being carried out at a rate substantially equal tothe rate of extrusion of molten composition.

i 13, In a process for the melt spinning of structures from a molten organic filament-forming composition, the steps comprising passing small, solid particles oi. said composition on to a heated surface to melt the same, passing an oxygen-free gas in a plurality of paths through said particles,

extruding the resulting molten composition, the melting of said composition being carried out at a rate substantially equal to the rate of extrusion of molten composition.

GEORGE DE wn'r GRAVES. 

